Methods of Manufacture MEMS Devices

ABSTRACT

Micro-electromechanical system (MEMS) devices and methods of manufacture thereof are disclosed. In one embodiment, a MEMS device includes a first semiconductive material and at least one trench disposed in the first semiconductive material, the at least one trench having a sidewall. An insulating material layer is disposed over an upper portion of the sidewall of the at least one trench in the first semiconductive material and over a portion of a top surface of the first semiconductive material proximate the sidewall. A second semiconductive material or a conductive material is disposed within the at least one trench and at least over the insulating material layer disposed over the portion of the top surface of the first semiconductive material proximate the sidewall.

This is a divisional application of U.S. application Ser. No.12/853,814, which was filed on Aug. 10, 2010, which is a continuationapplication of U.S. application Ser. No. 12/013,174, which was filed onJan. 11, 2008, both of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to the fabrication ofmicro-electromechanical system (MEMS) devices, and more particularly tothe fabrication of resonators and other moveable elements of MEMSdevices.

BACKGROUND

MEMS devices comprise a relatively new technology that combinessemiconductors with very small mechanical devices. MEMS devices aremicro-machined sensors, actuators, and other structures that are formedby the addition, subtraction, modification, and patterning of materialsusing techniques originally developed for the integrated circuitindustry. MEMS devices are used in a variety of applications, such as insensors for motion controllers, inkjet printers, airbags, microphones,and gyroscopes. The applications that MEMS devices are used in continueto expand and now include applications such as mobile phones,automobiles, global positioning systems (GPS), video games, consumerelectronics, automotive safety, and medical technology, as examples.

Manufacturing MEMS devices is challenging in many aspects. Fabricatingsmall moving parts of MEMS devices with lithography processes used insemiconductor technology has limitations in some applications. Reducingthe size of spaces between moving and stationary parts of MEMS devicesis limited to minimum feature sizes that are printable using aparticular lithography system and process, for example.

Thus, what are needed in the art are improved structures for MEMSdevices and methods of manufacture thereof.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by embodiments of thepresent invention, which provide novel MEMS devices and methods ofmanufacture thereof, wherein a sacrificial insulating material layer isused to form novel MEMS structures having sub-lithographic dimensions.

In accordance with an embodiment of the present invention, a MEMS deviceincludes a first semiconductive material and at least one trenchdisposed in the first semiconductive material. The at least one trenchhas a sidewall. An insulating material layer is disposed over an upperportion of the sidewall of the at least one trench in the firstsemiconductive material and over a portion of a top surface of the firstsemiconductive material proximate the sidewall. A second semiconductivematerial or a conductive material is disposed within the at least onetrench and at least over the insulating material layer disposed over theportion of the top surface of the first semiconductive materialproximate the sidewall.

The foregoing has outlined rather broadly the features and technicaladvantages of embodiments of the present invention in order that thedetailed description of the invention that follows may be betterunderstood. Additional features and advantages of embodiments of theinvention will be described hereinafter, which form the subject of theclaims of the invention. It should be appreciated by those skilled inthe art that the conception and specific embodiments disclosed may bereadily utilized as a basis for modifying or designing other structuresor processes for carrying out the same purposes of the presentinvention. It should also be realized by those skilled in the art thatsuch equivalent constructions do not depart from the spirit and scope ofthe invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1 through 4 show cross-sectional views of a method ofmanufacturing a MEMS device at various stages in accordance with anembodiment of the present invention, wherein a thin insulating materiallayer is used to form a space or gap between two semiconductivefeatures;

FIGS. 5 through 9 show cross-sectional views of a method ofmanufacturing a MEMS device at various stages in accordance with anembodiment of the present invention;

FIG. 10 shows a top view of the MEMS device shown in FIG. 9, wherein theMEMS device comprises a rectangular-shaped resonator;

FIGS. 11 through 13 show cross-sectional views of a method ofmanufacturing a MEMS device at various stages in accordance with anotherembodiment of the present invention, wherein the thin insulatingmaterial layer used to form the gap comprises a greater thickness on topsurfaces than on sidewalls of features;

FIGS. 14 through 16 show cross-sectional views of a method ofmanufacturing a MEMS device at various stages in accordance with yetanother embodiment of the present invention, wherein the thin insulatingmaterial layer used to form the gap comprises a greater thickness onsidewalls of features than on top surfaces; and

FIG. 17 shows a top view of yet another embodiment of the presentinvention, wherein a MEMS device comprises a circular-shaped resonator.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the preferredembodiments of the present invention and are not necessarily drawn toscale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of various embodiments of the invention arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

MEMS resonators offer significant advantages compared to quartzresonators in terms of size, shock resistance, electro-magneticcompatibility performance, and integratability into complementary metaloxide semiconductor (CMOS) circuitry. One challenge in MEMS devices isthe high motional resistance of the device compared to quartz, whichinhibits direct replacement of a quartz resonator by a silicon resonatorin some applications. In addition, high voltages between the electrodesare often needed to obtain a sufficient signal.

Embodiments of the invention provide structures for electrostaticallyactuated silicon MEMS resonators and methods of fabrication thereof. Thenovel MEMS devices comprise sub-lithographic vertical gaps havingdimensions as small as a few nanometers between crystalline siliconelectrodes. The MEMS devices exhibit high resonator quality factors andexcellent electrical coupling factors, resulting in low motionalresistance values for MEMS resonators and low actuation voltagescompatible with standard CMOS circuitry.

The present invention will be described with respect to embodiments inspecific contexts, namely implemented in MEMS devices comprisingmoveable elements that comprise resonators. Embodiments of the inventionmay also be implemented in other applications such as MEMS devicescomprising sensors, actuators, accelerometers, and other MEMS structureshaving floating or moveable parts and elements, for example.

Embodiments of the present invention achieve technical advantages byproviding novel MEMS devices and methods of manufacture thereof. FIGS. 1through 4 show cross-sectional views of a method of manufacturing a MEMSdevice 100 at various stages in accordance with an embodiment of thepresent invention, wherein a thin insulating material layer is used toform a space or gap between two semiconductive features, or between asemiconductive feature and a conductive feature.

Referring first to FIG. 1, to fabricate the MEMS device 100, a workpiece102 is provided. The workpiece 102 may include a semiconductor substrate104 or body comprising silicon or other semiconductor materials coveredby an insulating layer 106, for example. The workpiece 102 may alsoinclude other active components or circuits, not shown. The workpiece102 may include other conductive layers or other semiconductor elements,e.g., transistors, diodes, etc. Compound semiconductors, GaAs, InP,Si/Ge, or SiC, as examples, may be used in place of silicon. Thesubstrate 104 preferably comprises single crystal silicon, in someembodiments, for example, although alternatively the substrate 104 maycomprise amorphous silicon or polycrystalline silicon (polysilicon).

The workpiece 102 includes an insulating layer 106 disposed over thesubstrate 104. The insulating layer 106 preferably comprises a thicknessof about 500 nm, for example, although alternatively, the insulatinglayer 106 may comprise other dimensions. The insulating layer 106 maycomprise silicon dioxide, silicon nitride, or combinations thereof,although other insulators may also be used. The insulating layer 106 isalso referred to herein as a buried oxide layer.

A semiconductive material 108 is disposed over the insulating layer 106.The semiconductive material 108 may comprise a thickness of about 1 to20 μm, and in some applications may comprise a thickness of about 10 μm,for example. The semiconductive material 108 preferably comprisessimilar materials as described for the substrate 104, for example.Alternatively, the semiconductive material 108 may comprise othermaterials and dimensions. In some embodiments, the semiconductivematerial 108 preferably comprises single crystal silicon. Thesemiconductive material 108 may also comprise amorphous silicon orpolysilicon. The semiconductive material 108 is also referred to hereinas a first semiconductive material.

The workpiece 102 preferably comprises a silicon-on-insulator (SOI)substrate in some embodiments, for example. Alternatively, a substrate104 comprising bulk silicon may be provided, the insulating layer 106may be formed over the substrate 104, and the first semiconductivematerial 108 may be formed over the insulating layer 106. The workpiece102 includes the substrate 104, the insulating layer 106, and the firstsemiconductive material 108.

At least one trench 110 is formed in the first semiconductive material108, as shown in FIG. 1. Only one trench 110 is shown in FIGS. 1 through4; however, preferably a plurality of trenches 110 is simultaneouslyformed across the surface of the workpiece 102, for example. The trench110 may be formed by depositing a layer of photosensitive material (notshown) over the workpiece 102, patterning the layer of photosensitivematerial using a lithography mask and a lithography system (also notshown), developing the layer of photosensitive material, and using thelayer of photosensitive material as a mask while exposed portions of thesemiconductive material 108 are etched away.

The trench 110 preferably comprises a width of about several hundreds ofnm to about one μm or greater, and a depth comprising the entirethickness of the semiconductive material 108, for example.Alternatively, the trench 110 may comprise other dimensions.

The trench 110 is preferably formed in a first region 112 of theworkpiece 102. The first region 112 of the workpiece 102 may comprise aregion where an electrode or other element of a MEMS device 100 will beformed, for example. The first region 112 of the workpiece 102preferably comprises a region where a portion of the firstsemiconductive material 108 will remain adhered or attached to thesubstrate 104, in some embodiments. The first region 112 is locatedadjacent a second region 114 of the workpiece 102, as shown. The secondregion 114 comprises a region where supportive material around a portionof the semiconductive material 108 will be removed later. The secondregion 114 is also referred to herein as a release region, for example.The second region 114 comprises a region where a resonator or othermoveable element of the MEMS device 100 will be formed, for example.

The at least one trench 110 formed in the first semiconductive material108 comprises a first sidewall, e.g., the left sidewall shown in FIG. 1,and a second sidewall opposite the first sidewall, e.g., the rightsidewall in FIG. 1. After the trench 110 is formed, the top surface ofthe buried oxide layer 106 at the bottom of the trench 110 is leftexposed, as shown.

An insulating material layer 115 is formed over the top surface of thefirst semiconductive material 108, the first and second sidewalls of theat least one trench 110 in the first semiconductive material 116, andthe exposed top surface of the buried oxide layer 106, as shown in FIG.2. The insulating material layer 115 comprises a sacrificial materiallayer in the second region 114 of the workpiece 102. The insulatingmaterial layer 115 will be removed later from the second region 114 andfrom portions of the first region 112. Portions of the insulatingmaterial layer 115 will remain proximate and lining the first sidewallto adhere a second semiconductive material 116 to the firstsemiconductive material 108 in the first region 112, to be describedfurther herein. The insulating material layer 115 is also referred toherein as a second insulating material layer, e.g., with respect to theembodiment shown in FIGS. 5 through 9.

Referring again to FIG. 2, the insulating material layer 115 preferablycomprises silicon dioxide or silicon nitride deposited as a very thinfilm and having a thickness of about 100 nm or less in some embodiments,for example. The insulating material layer 115 may be formed by thinfilm deposition or by an oven process such as oxidation or nitridation,as examples. The insulating material layer 115 may also be depositedusing low pressure chemical vapor deposition (LPCVD) or atomic layerdeposition (ALD), as examples. The insulating material layer 115 maycomprise LPCVD tetra ethyl oxysilane (TEOS), for example. The insulatingmaterial layer 115 may comprise other materials and dimensions, and maybe deposited using other methods, for example.

In some embodiments, the insulating material layer 115 is conformal,comprising substantially the same dimension on top surfaces and on thesidewalls of the trench 110. In other embodiments, the insulatingmaterial layer 115 is non-conformal, to be described further herein withrespect to the embodiments shown in FIGS. 11 through 16.

A material 116 is disposed over the insulating material layer 115. Thematerial 116 is also referred to herein as a second semiconductivematerial or a conductive material 116 in some embodiments, for example.The material 116 fills the at least one trench 110 and covers theinsulating material layer 115. The material 116 may comprise a thicknessof about 20 to 100 nm or greater above a top surface of the insulatingmaterial layer 115, e.g., over the top surface of the firstsemiconductive material 108, for example, although alternatively, thematerial 116 may comprise other dimensions. The material 116 preferablycomprises a material resistant to a subsequent etch process for thesacrificial layer, e.g., the insulating material layer 115.

The material 116 may comprise a second semiconductive materialcomprising a semiconductor material such as polysilicon, althoughalternatively, the second semiconductive material layer 116 may compriseother materials, such as amorphous or crystalline silicon, as examples.The second semiconductive material 116 may be doped to increase theconductivity. In some embodiments, the second semiconductive material116 preferably comprises polysilicon doped with a dopant such as As, B,or P to improve the conductivity, although alternatively, other dopantsmay also be used. The second semiconductive material 116 may comprisein-situ doped polysilicon deposited using LPCVD or other methods, forexample. In other embodiments, the second semiconductive material 116may comprise amorphous or single crystal silicon, for example.

The material 116 may also comprise a conductive material in someembodiments. The conductive material 116 may comprise a metal such as W,Al, or other metals compatible with the processing methods of the MEMSdevice 100, for example. The conductive material 116 may also includeone or more liners, for example, combined with one or more layers oralloys of these metals.

The second semiconductive material or conductive material 116 ispatterned using a layer of photosensitive material and a lithographyprocess, removing portions of the second semiconductive material orconductive material 116 from over the top surface of the insulatingmaterial layer 115, as shown in FIG. 2. The second semiconductivematerial or conductive material 116 may be patterned using a wetchemical etching process, for example, although other methods may alsobe used. The second semiconductive material or conductive material 116is left remaining within the at least one trench 110 and over a portionof the insulating material layer 115 on the top surface of the firstsemiconductive material 108 proximate at least the first sidewall of theat least one trench 110.

For example, after patterning, the second semiconductive material orconductive material 116 preferably extends over the first semiconductivematerial 108 from the first sidewall by a dimension d₁ proximate thefirst sidewall, e.g., on the left of the trench 110. Dimension d₁ maycomprise about 0.5 to 5 μm, for example, although dimension d₁ mayalternatively comprise other amounts. Dimension d₁ is also referred toherein as a first dimension. Dimension d₁ is preferably relatively wideso that a portion of the insulating material layer 115 will remainbeneath the second semiconductive material or conductive material 116after the subsequent etch process of the insulating material layer 115,to be described further herein.

The second semiconductive material or conductive material 116 preferablyextends over the first semiconductive material 108 from the secondsidewall by a dimension d₂ proximate the second sidewall, e.g., on theright of the trench 110. Dimension d₂ may comprise about 400 nm or less,for example, although dimension d₂ may alternatively comprise otheramounts. Dimension d₂ is also referred to herein as a second dimension.The second semiconductive material or conductive material 116 may extendabove the top surface of the first semiconductive material 108 by about10 to 100 nm or greater, for example.

Dimension d₁ is preferably larger than dimension d₂. In someembodiments, dimension d₁ is greater than dimension d₂ by about 50% orgreater, for example. The relative size of dimensions d₁ and d₂ ispreferably controlled to ensure that a predetermined amount or portionof the insulating material layer 115 remains beneath the secondsemiconductive material or conductive material 116 after the subsequentetch process of the insulating material layer 115, for example.

Because of lithography variations, the amount or dimension d₂ that thesecond semiconductive material or conductive material 116 extends overthe top surface of the first semiconductive material 108 proximate thesecond sidewall may vary, e.g., from edge 118 to edge 120, as shown inphantom in FIG. 2. However, preferably, the second semiconductivematerial or conductive material 116 edge 118 or 120 resides at leastover the insulating material layer 115 disposed along the secondsidewall, in accordance with embodiments of the present invention. Morepreferably, the edge 118 or 120 of the second semiconductive material orconductive material 116 is disposed over a portion of the firstsemiconductive material 108, for example. Dimension d₂ is preferably apositive value in accordance with some embodiments of the presentinvention, for example; however, alternatively, dimension d₂ may also bezero.

In accordance with embodiments of the present invention, the edge of theactive gap 124 trench to be etched later is carefully defined, in orderto well-define the edge of the lever of the resonator or moveableelement 130 (see FIG. 3) formed from the first semiconductive material108 on the right side of FIG. 2 in the release region 114. Lithographyvariations, e.g., from edge 118 to 120 shown in FIG. 2, are preferablytaken into account in the definition of the edge of the active gap 124.To achieve this, the electrode or second semiconductive material orconductive material 116 is defined to have the small overlap ofdimension d₂ comprising about 100 to 400 nm in some embodiments,depending on the process technology used, with the underlying device,e.g., over the first semiconductive material 108. In contrast to theactive gap 124, the electrically inactive gap 122 is protected from theetchant of the subsequent etch process used to remove the insulatingmaterial layer 115 from the active gap 124 by the large overlapcomprising dimension d₁ which comprises about 0.5 μm to several, e.g.,5, μam between the electrode or second semiconductive material orconductive material 116 and the device layer or first conductivematerial 108 proximate the inactive gap 122. For example, the overlap onthe left side comprising dimension d₁ is preferably designed to be muchwider than the height of the active gap 124, e.g., wherein the height ofthe active gap 124 is substantially the same as the thickness of thefirst semiconductive material 108, in accordance with some embodimentsof the present invention.

Portions of the insulating material layer 115 are then removed using anetch process, as shown in FIG. 3. Region 122 comprising the insulatingmaterial layer 115 proximate the first sidewall comprises an inactivegap, and region 124 proximate the second sidewall comprises an activegap. At least a portion of the insulating material layer 115 is leftremaining in the inactive gap 122, and preferably all of the insulatingmaterial layer 115 is removed from the active gap 124. The active gap124 is also referred to herein as a first gap 124, for example.

For example, after the patterning of the second semiconductive materialor conductive material 116, the MEMS device 100 is subjected to an etchprocess, e.g., a wet chemical etching process, to remove portions of theinsulating material layer 115. Alternatively, other etch methods may beused to remove portions of the insulating material layer 115. The etchprocess removes all of the insulating material layer 115 from theexposed top surface of the first semiconductive material 108. Theetchant of the etch process also enters into the openings 132 on theleft and right side of the second semiconductive material or conductivematerial 116, e.g., beneath the second semiconductive material orconductive material 116, removing portions of the insulating materiallayer 115 beneath the second semiconductive material or conductivematerial 116.

For example, on the left side of FIG. 3, the insulating material layer115 is removed by an amount or dimension d₃ laterally from beneath thesecond semiconductive material or conductive material 116. A portion ofthe insulating material layer 115 is left remaining proximate the firstsidewall and inactive gap 122, as shown. The portion of the insulatingmaterial layer 115 left remaining comprises a dimension d₄ extendingalong the top surface of the first semiconductive material 108 away fromthe inactive gap 122. The removed insulating material layer 115 beneaththe second semiconductive material or conductive material 116 forms agap 125 comprising a dimension d₅ that comprises a dimensionsubstantially equal to the thickness of the insulating material layer115, for example. The gap 125 comprises a width extending away from theinactive gap 122 of dimension d₃.

The etch process also results in the removal of the insulating materiallayer 115 proximate the second sidewall and the active gap 124. Theetchant of the etch process enters the opening 132 proximate the secondsidewall, and results in the removal of the insulating material layer115 completely from the second sidewall and the active gap 124, as shownin FIG. 3. The thickness of the active gap 124 comprises a dimension d₆that is substantially equal to the thickness of the insulating materiallayer 115 on the second sidewall before the removal of the insulatingmaterial layer 115, for example.

At this point, the insulating material layer 115 may be left remainingbeneath the second semiconductive material or conductive material 116within the at least one trench 110, as shown. The insulating materiallayer 115 also resides along the first sidewall in the inactive gap 122and between the top surface of the first semiconductive material 108 andthe second semiconductive material or conductive material 116 proximatethe first sidewall, e.g., to the right of the gap 125.

The insulating material layer 115 comprises a thin sacrificial layerthat is used to define the thickness of the active gap 124 in accordancewith embodiments of the present invention. The thickness and dimensionsof the insulating material layer 115 determine the dimensions of gaps124 and 125 that are formed when portions of the insulating material 115are removed. For example, after depositing the insulating material layer115, the insulating material layer 115 may comprise a dimension d₅ ontop surfaces, e.g., on the top surface of the first semiconductivematerial 108 and on the bottom surface of the trench 110, e.g., on thetop surface of the buried oxide layer 106. The insulating material layer115 may comprise a dimension d₆ on sidewalls of the trench 110. In theembodiment shown in FIGS. 1 through 4, the insulating material layer 115is conformal and comprises substantially the same dimension on thesidewalls of the trench 110 and top surfaces of the first semiconductivematerial 108 and the buried oxide layer 106. Thus, dimension d₅ and d₆are substantially equal in this embodiment, for example.

When portions of the insulating material layer 115 are removed, the gap125 comprises dimension d₅ that was defined by the dimension d₅ of theinsulating material layer 115 on the top surface of the firstsemiconductive material 108 prior to the removal of the insulatingmaterial layer 115. The opening 132 proximate the first sidewall andinactive gap 122 also substantially comprises dimension d₅, for exampleLikewise, when portions of the insulating material layer 115 areremoved, the active gap 124 comprises dimension d₆ defined by thedimension d₆ of the insulating material layer 115 on the sidewalls ofthe first semiconductive material 108 prior to the removal of theinsulating material layer 115. The opening 132 proximate the secondsidewall and active gap 124 comprises dimension d₅, e.g., the dimensiond₅ of the insulating material layer 115 on the top surface of the firstsemiconductive material 108 proximate the second sidewall prior to theremoval of the insulating material layer 115.

Because the second semiconductive material or conductive material 116comprises a greater width (e.g., dimension d₁) over the firstsemiconductive material 108 extending away from the first sidewall thanthe width (e.g., dimension d₂) of the second semiconductive material orconductive material 116 over the first semiconductive material 108extending away from the second sidewall, advantageously, after the etchprocess for the insulating material layer 115, some of the insulatingmaterial layer 115 remains residing between the top surface of the firstsemiconductive material 108 and the second semiconductive material orconductive material 116 proximate the first sidewall. However, after theetch process, all of the insulating material layer 115 is removed frombetween the top surface of the first semiconductive material 108 and thesecond semiconductive material or conductive material 116 proximate thesecond sidewall, and all of the insulating material layer 115 lining thesecond sidewall is also removed. Again, the dimensions of d₁ and d₂ arepreferably designed to achieve these results, in accordance withembodiments of the present invention.

In accordance with some embodiments of the present invention, at leastone release hole 126 may be formed in the first semiconductive material108, as shown in FIG. 3, either before or after the etch process toremove the insulating material layer 115 from the second sidewall asshown in FIG. 3. Another etch process (or the same etch processpreviously described may be continued) may be used to remove additionalportions of the insulating material layer 115 and also a portion of theburied oxide layer 106, as shown in FIG. 4. Note that the buried oxidelayer 106 and the insulating material layer 115 preferably comprisematerials that may be etched using the same etch process, for example,in accordance with some embodiments of the present invention. The buriedoxide layer 106 is left residing beneath a portion of the firstsemiconductive material 108 beneath the second semiconductive materialor conductive material 116 which may comprise an electrode 116 in someembodiments.

The etchant of the etch process enters into the release holes 126 andinto the openings 132, removing the buried oxide layer 106 at least frombeneath the first semiconductive material 108 proximate the secondsidewall. The etch process may also remove at least a portion of theburied oxide layer 106 from beneath a portion of the secondsemiconductive material or conductive material 116 in the trench 110, asshown in FIG. 4. The buried oxide layer 106 comprises a thicknesscomprising a dimension d₇. The gap 128 formed beneath the firstsemiconductive material 108 proximate the second sidewall and active gap124 in the second region 114 comprises a dimension d₇ that issubstantially equal to the thickness of the buried oxide layer 106, forexample.

In the first region 112, the insulating material layer 115 may also beremoved from between at least a portion of the second semiconductivematerial or conductive material 116 and the substrate 104 in the trench110, forming a gap 134 comprising a dimension (d₅+d₇) that issubstantially equal to the dimensions of the insulating material layer115 and the buried oxide layer 106 prior to their removal, for example.

The gap 134 formed beneath the second semiconductive material orconductive material 116 is also referred to herein as a second gap 134,for example. The gap 128 formed beneath the first semiconductivematerial 108, e.g., beneath a moveable portion of the firstsemiconductive material 108 is also referred to herein as a third gap128, for example. The moveable portion of the first semiconductivematerial 108 in the second region 114 is also referred to herein as amoveable element 130 or resonator 130 herein, for example.

The openings 132 may be smaller than the release openings 126 in someembodiments, for example, so that only a small portion of the etchantenters the openings 132, and therefore only a small amount of theinsulating material layer 115 may be removed proximate the firstsidewall or inactive gap 122 during the portion of the etch process usedto remove a portion of the buried oxide layer 106.

After the etch process (or etch processes), the first semiconductivematerial 108 proximate the second sidewall or active gap 122, e.g., onthe right side of the figure, has been completely released. Thus, thereleased first semiconductive material 108 in the second region 114comprises a moveable element 130 of the first semiconductive material108 that is fully released, floating within the right side of the secondsemiconductive material or conductive material 116 and the substrate104. Advantageously, a portion of the second semiconductive material orconductive material 116 remains residing over the edge of the moveableelement 130, e.g., by dimension d₂ in some embodiments, retaining themoveable element 130 vertically within the MEMS device 100.Alternatively, dimension d₂ may comprise zero, so that the moveableelement 130 may be elevated above the top surface of the MEMS device 100during operation, e.g., upwardly along the right edge of the secondsemiconductive material or conductive material 116.

Advantageously, the second semiconductive material or conductivematerial 116 is disposed in close proximity to the moveable element 130,providing lateral support for the moveable element 130 while beingspaced apart by the dimension d₆ of the active gap 124, and optionallyalso providing vertical support while being spaced apart by thedimension d₅ of the opening 132, which is also the dimension of thespace between the second semiconductive material or conductive material116 and the moveable element 130. The moveable element 130 is notconnected to the substrate 104 and may move freely within the MEMSdevice 100. The second semiconductive material or conductive material116 proximate the moveable element 130 in the vertical and/or horizontaldirection may function as a mechanical stop for the moveable element130, or may prevent damage to the moveable element 130 and MEMS device100 during handling, by limiting or controlling the movement of themoveable element 130, for example. The moveable element 130 is limitedto movement within the active gap 124 and beneath the opening 132, ifdimension d₂ is greater than zero, for example. The moveable element 130is also referred to herein as a resonator or an oscillating element, forexample.

The second semiconductive material or conductive material 116 maycomprise an electrode of the MEMS device 100 in some embodiments, forexample. Advantageously, the electrode 116 is attached to the workpiece102 by a portion of the insulating material layer 115 along the firstsidewall, e.g., at 136 and also on the top surface of the firstsemiconductive material 108 proximate the first sidewall, e.g., at 138.The insulating material layer 115 adhering the electrode 116 to theworkpiece 102 along the first sidewall has a dimension substantiallyequal to the thickness of the first semiconductive material 108 less thedimension d₅ of a portion of the gap 134. The insulating material layer115 adhering the electrode 116 to the workpiece 102 proximate the firstsidewall on the top surface of the first semiconductive material 108 hasa width or dimension d₄. The attached electrode 116 provides excellentstructural stability for the electrode, or second semiconductivematerial or conductive material 116 of the MEMS device 100.

Because the thin insulating material layer 115 is used to define thethickness of the gap 124 and opening 132, very small dimensions for theactive gap 124 and opening 132 may be achieved, providing improvedelectromechanical coupling between the electrode 116 and the moveableelement 130 in accordance with embodiments of the present invention. Forexample, the thin insulating material layer 115 may advantageously beformed such that the insulating material layer 115 has sub-lithographicresolution dimensions, e.g., smaller than a minimum feature size than ifthe gap 124 was printed or formed using the lithography system andprocesses used to form other material layers of the MEMS device 100.

Note that a single etch process may be used to release the firstsemiconductive material 108 in the release region 114 of the MEMS device100. For example, FIG. 3 may show a MEMS device 100 at a point in themanufacturing process partially through the etch process, and FIG. 4 mayshow the MEMS device 100 at the completion of the etch process.

The moveable element 130 preferably comprises a resonator in accordancewith some embodiments of the present invention. The moveable element 130may also comprise other movable parts and elements used in MEMS devices100, for example. The moveable element 130 may comprise an oscillatingelement, an actuator, a sensor, a switch, an accelerometer, or othertypes of movable elements, as examples.

Only one side of the moveable element 130 is shown in the embodimentillustrated in FIGS. 1 through 4; however, other sides of the moveableelement 130 may also be released in accordance with embodiments of thepresent invention.

For example, FIGS. 5 through 9 show cross-sectional views of a method ofmanufacturing a MEMS device 200 at various stages in accordance with anembodiment of the present invention, wherein at least two opposing sidesof a moveable element 230 are released. Like numerals are used for thevarious elements that were used to describe FIGS. 1 through 4. To avoidrepetition, each reference number shown in FIGS. 5 through 9 is notdescribed again in detail herein. Rather, similar materials arepreferably used for the various material layers x02, x04, x06, x08,etc., as were described for FIGS. 1 through 4, where x=1 in FIGS. 1through 4 and x=2 in FIGS. 5 through 9. As an example, the preferred andalternative materials and dimensions described for the workpiece 102 inthe description for FIGS. 1 through 4 are preferably also used for theworkpiece 202 shown in FIGS. 5 through 9.

In this embodiment, the insulating material layer 215 (see FIG. 8) maycomprise a second insulating material layer 215, and an optional firstinsulating material layer 240 may be formed over the workpiece 202, asshown in FIG. 5, before patterning the first semiconductive material 208with a plurality of trenches 210 a, 210 b, 244 a, and 244 b, as shown inFIG. 6. The first insulating material layer 240 preferably comprisessilicon dioxide in some embodiments, for example. The first insulatingmaterial layer 240 preferably comprises the same material as the secondinsulating material layer 215 and/or the same material as the buriedoxide layer 206 in some embodiments. The first insulating material layer240 preferably comprises a material etchable using the same etchant andthe same etch process as the second insulating material layer 215 and/orthe same material as the buried oxide layer 206, in some embodiments.Alternatively, the first insulating material layer 240 may comprise adifferent material than the second insulating material layer 215 orburied oxide layer 206, in other embodiments. The first insulatingmaterial layer 240 may comprise silicon nitride, silicon oxynitride, orother insulating materials, as examples. The first insulating materiallayer 240 preferably comprises a thickness of about 50 nm or less, forexample, although alternatively, the first insulating material layer 240may comprise other dimensions. The first insulating material layer 240may be deposited by CVD, LPCVD, ALD, or physical vapor deposition (PVD),as examples, although other methods may also be used to form the firstinsulating material layer 240.

The first insulating material layer 240 is used as a hard mask topattern the first semiconductive material 208 with trenches. Forexample, a layer of photoresist 242 is formed over the first insulatingmaterial layer 240, and the layer of photoresist 242 is patterned usinga lithography mask with the desired pattern for trenches 210 a, 210 b,244 a, and 244 b. The layer of photoresist 242 is used as a mask topattern the first insulating material layer 240, and then the firstinsulating material layer 240, or both the first insulating materiallayer 240 and the layer of photoresist 242, are used as a mask toprotect the first layer of semiconductive material 208 while exposedportions of the first layer of semiconductive material 208 are etchedaway, forming trenches 210 a, 210 b, 244 a, and 244 b in the first layerof semiconductive material 208 and also the first insulating materiallayer 240, as shown in FIG. 6.

In this embodiment, trenches 210 a and 210 b comprise trenches whereelectrodes 216a and 216b, respectively, will be formed, and optionaltrenches 244 a and 244 b may comprise areas that will remain trenches inthe finished structure. Alternatively, trenches 244 and 244 b may not beformed in the MEMS device 200, for example.

The second insulating material layer 215 is then deposited over thepatterned first insulating material layer 240, over the sidewalls of thefirst semiconductive material 208, and the top surface of the buriedoxide layer 206 exposed at the bottom surface of the trenches 210 a, 210b, 244 a, and 244 b, also shown in FIG. 6.

The second semiconductive material or conductive material 216 is thendeposited over the second insulating material layer 215, as shown inFIG. 7. The second semiconductive material or conductive material 216 ispatterned using lithography, leaving portions of the secondsemiconductive material or conductive material 216 a and 216 b remainingin the trenches 210 a and 210 b, respectively, forming electrodes. Aportion of the second semiconductive material or conductive material 216c may also be left remaining in other areas of the MEMS device 200, asshown. The second semiconductive material or conductive material 216 isremoved from trenches 244 a and 244 b. The first semiconductive material208 disposed between the trenches 210 a and 210 b will comprise themoveable element 230 of the MEMS device 200 in this embodiment. Releaseholes 226 may be formed in the moveable element 230, e.g., by patterningthe first semiconductive material 208 using lithography, e.g.,optionally using the first insulating material layer 240 and the secondinsulating material layer 215 as a hard mask.

One or more etch processes are used to etch away portions of the secondinsulating material layer 215, the buried oxide layer 206, andoptionally also the first insulating material layer 240, leaving thestructure shown in FIG. 9. If the first insulating material layer 240comprises the same or similar materials as the second insulatingmaterial layer 215 and the buried oxide layer 206, the openings 232 aremade wider by the amount of the thickness or dimension d₈ of the firstinsulating material layer 240, facilitating the etch process to form theactive gaps or first gaps 224. Thus, the first insulating material layer240 may be used to increase the space, e.g., the openings 232, betweenthe first semiconductive material 208 and the portions of the secondsemiconductive material or conductive material 216 a and 216 b (and alsosecond semiconductive material or conductive material 216 c) residingover the first semiconductive material 208, advantageously.

In this embodiment, two electrodes 216 a and 216 b are formedsymmetrically about a moveable element 230. The buried oxide layer 206is preferably completely removed beneath the moveable element 230,forming the third gap 228, so that the moveable element 230 may movefreely within the MEMS device 200. At least a portion of the buriedoxide layer 206 may also be removed from beneath the secondsemiconductive material or conductive material 216 a and 216 b, forexample, forming the second gaps 234 within trenches 210 a and 210 b.Advantageously, the active gaps 224 of the MEMS device 200 are verynarrow, comprising a dimension d₆, due to the thinness of thesacrificial material comprising the second insulating material layer 215that was used to form the active gaps 224. In some embodiments, theelectrodes 216 a and 216 b preferably extend over the moveable element230 by a dimension d₂ to function as a mechanical stop above edges ofthe moveable element 230, e.g., in the vertical direction within theMEMS device 200, for example.

Because the active gaps 224 and the inactive gaps 222 are formed thesame insulating material layer 215 on sidewalls of the trenches 210 aand 210 b, the active gaps 224 and the inactive gaps 222 comprisesubstantially the same dimension or thickness d₆. The inactive gaps 222are at least partially filled with the insulating material layer 215,for example, which provides attachment of the second semiconductivematerial or conductive material 216 a and 216 b to the workpiece 202.

FIG. 10 shows a top view of the MEMS device 200 shown in FIG. 9. Themoveable element 230 may comprise a resonator in some embodiments, forexample. The resonator 230 may be anchored at one or more locations. Forexample, in the embodiment shown in FIG. 10, the resonator 230 comprisesan anchor 246 disposed at two opposing ends that is coupled to theworkpiece 202 underlying material layers. However, between the twoanchors 246, the resonator 230 may move freely within the active gap224. Alternatively, the resonator 230 may comprise an anchor 246 only atone end, for example, not shown.

In the previous embodiments described herein, the insulating materiallayers 115 and 215 comprise a conformal material layer. The insulatingmaterial layers 115 and 215 may also be non-conformal. For example,FIGS. 11 through 13 show cross-sectional views of a method ofmanufacturing a MEMS device 300 at various stages in accordance withanother embodiment of the present invention, wherein the thin insulatingmaterial layer 315 used to form the inactive and active gaps 322 and 324comprises a greater thickness or dimension d₅ on top surfaces than onsidewalls of the trenches 310, which have a thinner dimension d₆. Again,like numerals are used for the various elements that were used todescribe the previous figures, and to avoid repetition, each referencenumber shown in FIGS. 11 through 13 is not described again in detailherein.

In this embodiment, the insulating material layer 315 may be formedusing a non-conformal deposition process that results in the insulatingmaterial layer 315 forming in a greater thickness d₅ on top surfaces.Forming the insulating material layer 315 may comprise using ananisotropic deposition process, leaving an insulating material layer 315comprising a greater thickness d₅ over the top surface of the firstsemiconductive material 308 and over the top surface of the buried oxidelayer 306 within the trenches 310 than over the first and secondsidewalls of the trenches 310 having dimension d₆, as shown in FIG. 11.This results in a wider opening 332 proximate the first and secondsidewalls of the trenches 310 shown in FIG. 12, which facilitates theetch process used to release the buried oxide layer 306 from portions ofthe MEMS device 300, shown in FIG. 13. Advantageously, the thickness ofthe insulating material layer 315 may be adjusted to achieve the desiredopening 332 size, for example.

FIGS. 14 through 16 show cross-sectional views of a method ofmanufacturing a MEMS device 400 at various stages in accordance with yetanother embodiment of the present invention, wherein the thin insulatingmaterial layer 415 used to form the inactive and active gaps 422 and 424comprises a greater thickness d₆ on sidewalls of features than on topsurfaces having a thinner dimension d₅. Again, like numerals are usedfor the various elements that were used to describe the previousfigures, and to avoid repetition, each reference number shown in FIGS.14 through 16 is not described again in detail herein.

The insulating material layer 415 may be conformal as deposited in thisembodiment, and an anisotropic etch process may be used to remove aportion of the insulating material layer 415 from over the top surfaceof the first semiconductive material 408 and also from over the buriedoxide layer 406. For example, after forming the insulating materiallayer 415, a method of manufacturing the MEMS device 400 may includeanisotropically etching the insulating material layer 415, leaving aninsulating material layer 415 comprising a greater dimension orthickness d₆ over the first and second sidewalls of the trench 410 thanover the top surface of the first semiconductive material 408 and thanover the top surface of the buried oxide layer 406 having dimension d₅.Note that the anisotropic etch process may result in tapered sidewallsat the corners and edges of the top of the trench 410, as shown inphantom in FIG. 14 at 450.

In this embodiment, the openings 432 proximate the inactive gap 422 andactive gap 424 are narrowed as shown in FIGS. 15 and 16. Advantageously,the openings 432 may be made narrower to limit the amount of insulatingmaterial layer 415 that is removed proximate the inactive gap 422,ensuring strong structural support for the electrodes formed from thesecond semiconductive material or conductive material 416, in someembodiments, as shown in FIG. 16.

Note that the optional first insulating material layer 240 shown inFIGS. 5 through 9 may also be implemented and included in theembodiments shown in FIGS. 11 through 13 and FIGS. 14 through 16, forexample, to provide further control of the dimensions d₅ of the openings332 and 432 proximate the inactive gaps 322 and 422 and the active gaps324 and 424, in accordance with embodiments of the present invention,not shown in the figures.

The amount of the sacrificial insulating material layer 115, 215, 315,and 415 that is removed, e.g., having dimensions d₅ and d₆, mayadvantageously be controlled by designing the size of the openings 132,232, 332, and 432 as desired, e.g., by controlling the dimension d₅ ordimension (d₅+d₈) using anisotropic deposition or etch processes for theinsulating material layers 115, 215, 315, and 415, and also by includingor not including the optional first insulating material layer 240comprising dimension d₈, for example.

The moveable elements 130, 230, 330, and 430 comprised of the firstsemiconductive material 108, 208, 308, and 408 described herein maycomprise a variety of shapes. The moveable elements 130, 230, 330, and430 may comprise the shape of a rectangle, square, octagon, polygon,circle, or ellipse in a top view of the MEMS devices 100, 200, 300, and400, as examples, although other shapes may also be used. The moveableelements 130, 230, 330, and 430 may also comprise the shape of a fork,e.g., similar to a tuning fork. The embodiment shown in FIG. 10illustrates a MEMS device 200 comprising a resonator 230 having arectangular shape, for example. As another example, FIG. 17 shows a topview of yet another embodiment of the present invention, wherein a MEMSdevice 500 comprises a circular-shaped resonator 530. The resonator 530may include one or more optional anchors 552 disposed above or below theresonator 530 in other material layers, as shown in phantom, forexample.

After the manufacturing process steps for the MEMS devices 100, 200,300, 400, and 500 described herein, other manufacturing process stepsmay then be completed to make electrical contact to portions of the MEMSdevices 100, 200, 300, 400, and 500, or to vacuum encapsulate the MEMSdevice 100, 200, 300, 400, and 500 structures, for example, not shown.

Embodiments of the present invention include MEMS devices 100, 200, 300,400, and 500 fabricated using the methods and comprising the novelstructures described herein. Embodiments of the present invention alsoinclude methods of fabricating the MEMS devices 100, 200, 300, 400, and500 described herein, for example.

Advantages of embodiments of the invention include providing methods offabricating MEMS devices 100, 200, 300, 400, and 500 wherein the movingsemiconductor portion 130, 230, 330, 430, or 530, e.g., which maycomprise a resonator 130, 230, 330, 430, or 530 or other moveable MEMSelement, is spaced closely to an adjacent semiconductor material, e.g.,second semiconductive material or conductive material 116, 216 a, 216 b,316, 416, and 516, which may comprise electrodes. A portion of thesecond semiconductive material or conductive material 116, 216 a, 216 b,316, 416, and 516 may reside over the edges of the resonators 130, 230,330, 430, or 530 in some embodiments, providing a mechanical stop forthe moveable elements 130, 230, 330, 430, or 530 within the MEMS devices100, 200, 300, 400, and 500.

The second semiconductive material or conductive material 116, 216 a,216 b, 316, 416, and 516 is spaced apart from the resonators 130, 230,330, 430, or 530 by a very narrow gap, e.g., the active gap 124, 224,324, 424, and 524 that may comprise a width of less than a minimumfeature size printable by the lithography system used to manufacture theMEMS devices 100, 200, 300, 400, and 500. The active gaps 124, 224, 324,424, and 524 and inactive gaps 122, 222, 322, 422, and 522 may comprisea thickness of about 100 nm or less in accordance with embodiments ofthe present invention, for example.

The close lateral proximity of the second semiconductive material orconductive material 116, 216 a, 216 b, 316, 416, and 516 to the moveableelements 130, 230, 330, 430, or 530 provides improved electromechanicalcoupling for the MEMS devices 100, 200, 300, 400, and 500. Because theactive gap 124, 224, 324, 424, and 524 is formed using a sacrificialthin insulating material layer 115, 215, 315, 415, and 515, a very smallgap 124, 224, 324, 424, and 524 may be achieved, for example.

Using a non-conformal sacrificial layer for the insulating materiallayers 115, 215, 315, 415, and 515 may provide further advantages insome applications. Using insulating material layers 115, 215, 315, 415,and 515 wherein the material on sidewalls is thinner than on topsurfaces may provide less parasitic capacitances in some applications,and may also be advantageous in applications where the floating pieces(e.g. the moveable elements 130, 230, 330, 430, and 530) require morelateral support from the anchoring electrodes 116, 216 a, 216 b, 316,416, and 516. Using insulating material layers 115, 215, 315, 415, and515 wherein the material on sidewalls is thicker than on top surfacesmay be advantageous in applications requiring more vertical support forthe anchoring electrodes 116, 216 a, 216 b, 316, 416, and 516, forexample.

Embodiments of the present invention are easily implementable inexisting manufacturing process flows for MEMS devices 100, 200, 300,400, and 500, with few additional processing steps being required forimplementation of the invention, for example. Very narrow gaps, e.g.,active gaps 124, 224, 324, 424, and 524 may be fabricated by the methodsdescribed herein. A high accuracy of the active gap 124, 224, 324, 424,and 524 dimension is achieved, because a deposition process, oxidation,or nitridation process is used to define the active gap 124, 224, 324,424, and 524 (e.g., by the formation of the sacrificial insulatingmaterial layer 115, 215, 315, 415, and 515), wherein variations in theactive gap 124, 224, 324, 424, and 524 dimension of about 1 nm or lessare achievable, for example.

Silicon resonator devices 100, 200, 300, 400, and 500 are describedherein having sub-100 nm vertical active gaps 124, 224, 324, 424, and524 dimensions between electrodes 116, 216 a, 216 b, 316, 416, and 516and a single crystalline resonator 130, 230, 330, 430, and 530structure. The moveable elements 130, 230, 330, 430, and 530 maycomprise a shape of a beam, wheel, plate, or other shapes, and may beimplemented in electrostatically driven MEMS devices 100, 200, 300, 400,and 500, for example. MEMS devices 100, 200, 300, 400, and 500 may befabricated using the techniques described herein that have a lowmotional resistance and a high quality factor, and that are adapted tooperate at standard CMOS compatible operating voltages.

Although embodiments of the present invention and their advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the invention as defined by the appended claims.For example, it will be readily understood by those skilled in the artthat many of the features, functions, processes, and materials describedherein may be varied while remaining within the scope of the presentinvention. Moreover, the scope of the present application is notintended to be limited to the particular embodiments of the process,machine, manufacture, composition of matter, means, methods and stepsdescribed in the specification. As one of ordinary skill in the art willreadily appreciate from the disclosure of the present invention,processes, machines, manufacture, compositions of matter, means,methods, or steps, presently existing or later to be developed, thatperform substantially the same function or achieve substantially thesame result as the corresponding embodiments described herein may beutilized according to the present invention. Accordingly, the appendedclaims are intended to include within their scope such processes,machines, manufacture, compositions of matter, means, methods, or steps.

1. A method of forming a micro-electromechanical system (MEMS) device,the method comprising: forming a buried oxide layer over a substrate;forming a first semiconductive material over the buried oxide layer;forming at least one trench in the first semiconductive material and theburied oxide layer, the at least one trench comprising a first sidewalland a second sidewall opposite the first sidewall; forming an insulatingmaterial layer over at least a portion of the first sidewall of the atleast one trench , wherein the insulating material layer is not an airgap; forming a second semiconductive material within the at least onetrench ; and forming a first gap in an upper portion of the at least onetrench, the first gap being formed between the second semiconductivematerial and the second sidewall of the at least one trench in the firstsemiconductive material.
 2. The method according to claim 1, wherein thefirst semiconductive material comprises single crystal silicon, whereinthe second semiconductive material comprises polysilicon.
 3. The methodaccording to claim 1, wherein the first semiconductive material formspart of a moveable element comprising a resonator, an oscillatingelement, an actuator, a sensor, a switch, or an accelerometer.
 4. Themethod according to claim 1, wherein forming the at least one trenchcomprises: forming a first trench adjacent a first side of a portion ofthe first semiconductive material, and forming a second trench adjacenta second side of the portion of the first semiconductive material, thesecond side being opposite the first side.
 5. The method according toclaim 4, further comprising: forming a second gap between the substrateand the second semiconductive material within a lower portion of the atleast one trench; and forming a third gap between the substrate and theportion of first semiconductive material between the first trench andthe second trench, wherein the portion of the first semiconductivematerial between the first trench and the second trench comprises amoveable element, and wherein the second semiconductive material on thefirst side and the second side of the moveable element within the firsttrench and the second trench, respectively, comprise electrodes.
 6. Themethod according to claim 5, wherein the moveable element substantiallycomprises a shape of a rectangle, square, octagon, polygon, circle,ellipse, or fork in a top view of the MEMS device.
 7. A method offabricating a micro-electromechanical system (MEMS) device, the methodcomprising: forming a oxide layer over a workpiece; forming a firstsemiconductive material over the oxide layer; forming a first trench inthe first semiconductive material and the oxide layer, the trenchcomprising a first sidewall and a second sidewall opposite the firstsidewall; forming an insulating material layer over the firstsemiconductive material, a first portion of the insulating materiallayer being formed over at least a portion of the first sidewall of thefirst trench, wherein the insulating material layer comprises an oxideor a nitride material; forming a conductive material within and over thefirst trench, the conductive material contacting the first portion ofthe insulating material layer; and forming a first gap in an upperportion of the first trench, the first gap being formed between theconductive material and the second sidewall of the first trench.
 8. Themethod according to claim 7, wherein the first semiconductive materialcomprises single crystal silicon, and wherein the conductive materialcomprises W, Al, at least one liner, or combinations thereof.
 9. Themethod according to claim 7, wherein the first semiconductive materialproximate the first gap comprises a moveable element comprising aresonator, an oscillating element, an actuator, a sensor, a switch, oran accelerometer.
 10. The method according to claim 7, wherein the firsttrench is adjacent a first side of a portion of the first semiconductivematerial, further comprising a second trench adjacent a second side ofthe portion of the first semiconductive material, the second side beingopposite the first side.
 11. The method according to claim 10, furthercomprising: forming a second gap between the workpiece and theconductive material within a lower portion of the first trench; andforming a third gap between the workpiece and the portion of firstsemiconductive material between the first trench and the second trench,wherein the portion of the first semiconductive material between thefirst trench and the second trench comprises a moveable element, andwherein the conductive material on the first side and the second side ofthe moveable element within the first trench and the second trench,respectively, comprise electrodes.
 12. The method according to claim 11,wherein the moveable element substantially comprises a shape of arectangle, square, octagon, polygon, circle, ellipse, or fork in a topview of the MEMS device.
 13. The method according to claim 10, furthercomprising forming a release hole within the portion of the firstsemiconductive material.
 14. A method of manufacturing amicro-electromechanical system (MEMS) device, the method comprising:providing a workpiece, the workpiece comprising a substrate, a buriedoxide layer disposed over the substrate, and a first semiconductivematerial disposed over the buried oxide layer, the first semiconductivematerial having a top surface; forming at least one trench in the firstsemiconductive material, exposing a top surface of the buried oxidelayer at a bottom of the at least one trench, the at least one trenchcomprising a first sidewall and a second sidewall opposite the firstsidewall; forming an insulating material layer over the first and secondsidewalls of the at least one trench, and the top surface of the buriedoxide layer; disposing a second semiconductive material or a conductivematerial over the insulating material layer; removing portions of thesecond semiconductive material or the conductive material therebyleaving the second semiconductive material or the conductive materialwithin the at least one trench; and removing the insulating materiallayer from over the second sidewall of the at least one trench.
 15. Themethod according to claim 14, wherein forming the insulating materiallayer comprises forming a conformal material.
 16. The method accordingto claim 14, wherein removing the portions of the second semiconductivematerial or the conductive material comprises: leaving an amount of thesecond semiconductive material or the conductive material having a firstdimension over the first semiconductive material proximate the firstsidewall; and leaving an amount of the second semiconductive material orthe conductive material having a second dimension over the firstsemiconductive material proximate the second sidewall, wherein the firstdimension is larger than the second dimension.
 17. The method accordingto claim 14, further comprising forming at least one release hole in thefirst insulating material proximate the second sidewall, and removing atleast the buried oxide layer at least from beneath the first insulatingmaterial proximate the second sidewall, wherein removing the buriedoxide layer further comprises removing at least a portion of the buriedoxide layer from beneath the second semiconductive material or theconductive material in the at least one trench.
 18. The method accordingto claim 17, wherein removing the buried oxide layer comprises forming aresonator or an oscillating element, further comprising forming ananchor proximate at least one end of the resonator or the oscillatingelement, above the resonator or the oscillating element, or below theresonator or the oscillating element.
 19. The method according to claim14, further comprising anisotropically etching the insulating materiallayer, after forming the insulating material layer, leaving aninsulating material layer comprising a greater thickness over the firstand second sidewalls of the at least one trench than over the topsurface of the first semiconductive material and the top surface of theburied oxide layer.
 20. The method according to claim 14, whereinforming the insulating material layer comprises using an anisotropicdeposition process, leaving an insulating material layer comprising agreater thickness over the top surface of the first semiconductivematerial and the top surface of the buried oxide layer than over thefirst and second sidewalls of the at least one trench.